5Gbit/5Gbit fiber so I was upgrading my network and went 10G over 2.5G because, well, it's awesome!
I simply size my network based on the storage speed.
I have a Raid 10 running and the disks hit ~450MB/s which is more than a 2.5 but less than a 5gbps threshold.
Sure, 10GE would cover things but, the expense for that on a laptop is a bit high as you need a TB 10GE dongle and those run about $300 where a 5GE dongle is only $70. I threw a quad port 5GE NIC into the server for $200 and bonded 2 ports to the ISP for redundancy and use the other 2 for AP / misc and the on board 2.5 as a spare.
The real question here is why you need 5GE ISP/WAN speeds. If it's just to have it, that's one thing but, it's a pricey upgrade for surfing the web and having a high sped test number. It does make quick work though of downloads for media. I used to have gig and found though that most hosts didn't even come close to providing enough bandwidth to utilize the full potential and typically only hit ~500-600mbps. On the rare occasion software update servers would be able to push data at line speed. In the end I switched to 5G FWA and cut the bill in half. Sure, it's a bit slower but, it works fine.